REFLECTOR: Performance

Thu May 9 11:23:34 CDT 2013

I still don't understand the drag mechanism for normal angle of exhaust 
being a drag.
Does anyone know where I can find NACA or other research on this?

On 5/9/2013 11:07 AM, Richard J. Gentil wrote:
> Geoff,
>
> If you make the exhaust change I would be very interested in your 
> results since mine currently exit straight down.
>
> Richard
>
> Sent from my iPhone 5
>
> On May 8, 2013, at 10:59 PM, Geoff Gerhardt <geoff.gerhardt at gmail.com 
> <mailto:geoff.gerhardt at gmail.com>> wrote:
>
>> Scott,
>>
>> Thanks - that was the insight I was looking for and what I suspected. 
>>  I would actually prefer to have the normal, shorter wing - I'd love 
>> the 15kts in speed and would gladly live with a little higher stall 
>> speed.
>>
>> Now, given that, I wonder if there's anything I could do that could 
>> improve my performance.  The two things that I'm considering are 
>> changing my exhaust config from exiting straight down to exiting 
>> inside the cowling at the prop.  I've heard some folks state they 
>> have seen significant improvements with that mod.  The other was an 
>> intake ram scoop - would that give me more MAP at altitude and a 
>> little more power?
>>
>> Thanks for all the performance comments/comparisons...keep them coming.
>>
>> Geoff
>>
>> On Wed, May 8, 2013 at 8:31 PM, Scott Baker <scottb33333 at gmail.com 
>> <mailto:scottb33333 at gmail.com>> wrote:
>>
>>     I notice that several responders are giving numbers for a
>>     Velocity Standard RG, while Geoff's aircraft is a Velocity 173
>>     (aka LW 'Long Wing').
>>     Velocity Standard models, with their smaller wings and reduced
>>     drag, are faster than their 173 brethren ... by 15 knots on
>>     average (with comparable engines and propellers).
>>     The factory V173FG trainer is hard pressed to see 145KTAS in
>>     cruise.  I think the RG version cruises between 155-160KTAS
>>     (about 15knots faster than the fixed gear model).
>>     These numbers are pretty close to what Geoff is reporting for his
>>     aircraft.
>>     Scott B.
>>
>>
>>
>>
>>     On 5/8/2013 10:38 AM, Geoff Gerhardt wrote:
>>>     Folks,
>>>
>>>     I'm getting pretty consistent performance out of my 173RG over
>>>     the last 8-9 months since initial flight testing.  My question
>>>     to you guys is, are the performance numbers I'm seeing typical,
>>>     or should I be seeing better performance?  Normally, on a cross
>>>     country, I'll fly b/w ~8-12,000', ~60deg LOP which typically has
>>>     me going 150kias at 8-8.5gph.  Full power, 160kias is about my
>>>     max speed.
>>>
>>>     I have a fixed-pitch Catto prop (66x74, design target 200mph @
>>>     2800RPM).  When I'm doing 160kts, my prop is spinning at
>>>     ~2800RPM.  That tells me that I have the power to spin the prop,
>>>     but may have air frame drag that's keeping me from seeing the
>>>     200mph predicted by Catto at 2800RPM.
>>>
>>>     I have a standard 200hp, Lyc IO-360, Lightspeed EI on one side,
>>>     Mag on the other.  Timing as per spec for both EI and Mag.
>>>      About 90hrs on the engine (rebuilt).  Compression/oil
>>>     consumption is normal.  Very stable performance from the engine.
>>>
>>>     My plane is fully finished and pretty tight.  Main/nose gear
>>>     doors are not hanging out and are reasonably well tucked in when
>>>     the gear is raised.  Main wing angles of incidence are spot on,
>>>     no rudder trimming was necessary to center the ball - she flies
>>>     nice and straight.
>>>
>>>     The factory predicts I should be able to cruise at 175kias -
>>>     that's just not possible with my current setup.  Can others with
>>>     Std Velocities relate the performance you are seeing?  Is this
>>>     as good as it gets, or does anyone have suggestions for things
>>>     to check to see if I can eek out a bit more speed?
>>>
>>>     Thanks.
>>>
>>>     Geoff
>>>
>>>
>>>
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